====== Computer Lab 05, Non-trivial loops ======


===== Practical work =====

==== Sum of digits in a string ====
Let s be a string containg several characters some of which may be digits.  Write a function that returns the sum of all digits in that string.

<code python>
def sum_digits_in_string(s):
    """Return sum of all digits in a string.
    :param s: string containing the digits and other characters
    :return: numeric value, sum of all digits

    Examples:
    >>> sum_digits_in_string('1')
    1
    >>> sum_digits_in_string('hi 1 hello 2')
    3
    >>> sum_digits_in_string('Values: 1.26, 2.3, 1.76')
    28
    """
</code>

==== Sum of decimal numbers in a string ====
Let s be a string containing decimal numbers separated by commas, e.g. s = '1.26,2.3,1.76'. Write a function that returns the sum of all decimal numbers in that string.

<code python>
def sum_decimals_in_string(s):
    """Return sum of decimal numbers in a string.
    :param s: string containing the decimal numbers separated by ','
    :return: float, sum of all decimals

    Examples:
    >>> sum_decimals_in_string('1.2')
    1.2
    >>> sum_decimals_in_string('1.2,3.4')
    4.6
    >>> sum_decimals_in_string('1,2,0.000001')
    3.000001
    """
</code>

==== Character triangles ====
Using nested loops, write function ''print_left_triangle(n_rows, char)'' which prints the triangle depicted below. E.g. when you call that function like this:

<code python>
>>> print_left_triangle(n_rows=5, char='T')
T
TT
TTT
TTTT
TTTTT
</code>

Again, using nested loops, write function ''print_right_triangle(n_rows, char)'' which prints the triangle depicted below. E.g. when you call that function like this:

<code python>
>>> print_right_triangle(n_rows=5, char='T')
    T
   TT
  TTT
 TTTT
TTTTT
</code>

==== Chemical compounds ====
Write a function ''combine_elements(el1, el2)'' which takes 2 iterables (e.g. lists) of chemical elements, and returns a list of all possible compounds that can arise by combining an element from the first list with an element from the second list.

<code python>
def combine_elements(el1, el2):
    """Return a list of possible compounds each containg a single element from both the first and second list.
    :param el1: list of strings, symbols of chemical elements for the first place of compound
    :param el2: list of strings, symbols of chemical elements for the second place of compound
    :return: list of strings, possible chemical compounds
    
    Example:
    >>> metals = 'Li Na K'.split()
    >>> halogens = 'F Cl Br'.split()
    >>> print(combine_elements(metals, halogens))
    ['LiF', 'LiCl', 'LiBr', 'NaF', 'NaCl', 'NaBr', 'KF', 'KCl', 'KBr']
    """
</code>

==== Production maximization ====
// Somewhat more complex task for more advanced students.//

Your small company produces wooden chairs and tables. Profit from a single chair is ''profit_per_chair'', profit from a single table is ''profit_per_table''. To build a single chair, you need to invest ''wood_per_chair'' units of wood and ''manhours_per_chair'' manhours of labour, to build a single table you need to invest ''wood_per_table'' units of wood and ''manhours_per_table'' manhours of labour. How many chairs and tables (''n_chairs'', ''n_tables'') should you produce per day to maximize your profit, if you can invest ''available_manhours'' manhours a day and ''available_wood'' units of wood a day, and if you want the numbers of chairs and tables to be integers?

Write a function that returns the optimal values given all the parameter values as arguments.

<code python>
def compute_optimal_production(profit_per_chair, profit_per_table, 
        wood_per_chair, wood_per_table, 
        manhours_per_chair, manhours_per_table, 
        available_wood, available_manhours):
    """Return numbers of chairs and tables to be produced per day to maximize profit.
    :param profit_per_chair: Company profit for a single chair produced.
    :param profit_per_chair: Company profit for a single table produced.
    :param wood_per_chair: Amount of wood required to build a single chair.
    :param wood_per_table: Amount of wood required to build a single table.
    :param manhours_per_chair: Amount of work required to build a single chair.
    :param manhours_per_table: Amount of work required to build a single chair.
    :param available_wood: Total amount of wood available for production each day.
    :param available_manhours: Total amount of work available each day.
    :return: (n_chairs, n_tables) tuple containing the optimal number of chairs and tables produced each day.
    
    Example:
    >>> profit_per_chair, profit_per_table = 20, 30
    >>> wood_per_chair, manhours_per_chair = 1, 3
    >>> wood_per_table, manhours_per_table = 6, 1
    >>> available_wood, available_manhours = 288, 99
    >>> print(compute_optimal_production(
            profit_per_chair, profit_per_table, wood_per_chair, wood_per_table,
            manhours_per_chair, manhours_per_table, available_wood, available_manhours))
    (18, 45) 
    """
</code>

Suggestion: Proceed in smaller steps. 
  * Create helper function to compute the total profit from x chairs and y tables. 
  * Create a helper function telling you, whether when producing x chairs and y tables, the available amount of wood is or is not exceeded. 
  * Create a helper function telling you, whether when producing x chairs and y tables, the available manhours are or are not exceeded. 
  * Compute the maximal number of chairs and tables that can be produced per day, if you decided to produce only chairs/only tables.
  * Then combine it all to complete function ''compute_optimal_production()''. Perform exhaustive search among all feasible pairs of values for ''n_chairs'' and ''n_tables''.

===== Homework =====
  * Finish all the above tasks.
  * Read [[http://openbookproject.net/thinkcs/python/english3e/modules.html|chapter 12]] of {[a4b99rph:Wenthworth]}.